<!DOCTYPE html>
<html>

<head>
    <meta charset="utf-8">
    <title>菜鸟教程(runoob.com)</title>
</head>

<body>

    <p>单击按钮将代码块循环执行5次。</p>
    <button onclick="myFunction()">点我</button>
    <p id="demo"></p>
    <script>
        function myFunction() {
            var x = "", i;
            for (i = 0; i < 5; i++) {
                x = x + "这个数字是" + i + "<br>";
            }
            document.getElementById("demo").innerHTML = x;
        }
    </script>

</body>

</html>